It's interesting, but to put this in OS4 at this stage would be impossible. It's apparently not far from finished, and obviously it wouldn't have Apple's blessing, and implementing MacOS's API without their help would be a mammoth task to do properly and would set back the release date much much further.
Also consider the price of new PPC Amiga hardware is similarly expensive to Apple's (and there's no G5s yet.) If you want to run MacOS (and OSX) software, you'll go for the Apple because that's the one that runs these programs flawlessly (again, look at WINE, it's far from perfect) and it has a nice pretty box to go in, and other Apple hardware standards that don't appear on A1/A1Lite boards.
Also, a note about file types, etc. None of the filetypes you mentioned are Windows 'native' in any way, they just happen to be the file types used by the most popular Windows programs. PDF for example was designed to be totally portable.
